How do I Convert MP3 to M4A on my Mac?

Apple has included the afconvert utility for years. It is a command line (e.g. Terminal) tool that as I have just done, will convert an .mp3 to .m4a audio file.

Place a sample .mp3 file on your Desktop and then open the Terminal application. Enter the following adjusting for your .mp3 filename, and at the end of the entered content, press return. Don't copy/paste this.

cd ~/Desktop
/usr/bin/afconvert ./foo.mp3 -o foo.m4a -q 127 -b 256000 -f m4af -d aac

You will find a foo.m4a audio file on you Desktop. More information about afconvert can be found here, and from the command line:

/usr/bin/afconvert -h
/usr/bin/afconvert -hf

For a visual interface more user friendly than the Terminal, you might consider launching the Mac App Store, and searching for audio converter. The first app, The Audio Converter has 2.1K reviews with an average of 4.5 stars. I do not use this tool so no vested interest.

Music app > Album > Song > File > Convert > Create ACC Version. No fancy apps required. You will then see a duplicate of the audio in the music app on your computer but it’ll take a few minutes to fully convert. You’re welcome :)

xAct is free wear and works extremely well in my experience.

http://xact.scottcbrown.org/

The free, open source Audacity will do the conversion for you.

you can use vlc media player it's free

4 Methods to Convert MP3 to M4A on Windows and Mac - VideoProc

Note that converting from one lossy format (MP3) to another (AAC) may result in loss of sound quality.

You don't get back the sound quality that you threw away when compressing the original audio to get the MP3, and the conversion to AAC may introduce more loss.

I guess that is a matter of individual hearing as the .mp3 audio that I converted to .m4a sounded identical when listed to via my Sony WH-1000XM4 headphones.

When converting either way, I use one of the many free, online services. But then, I'm not converting for professional standards - just so I can listen.